1. Field of the Invention
The present invention relates to an oxide thin film transistor, and more particularly, to a method of manufacturing an oxide thin film transistor not including an etch stop layer.
2. Discussion of the Related Art
Image display devices, which display a variety of information on a screen, are a core technology of information and communication and are becoming increasingly thinner, lighter, more portable, and higher in performance. In particular, as needs for flexible displays with spatiality and convenience increase, organic light emitting diode display devices, which control light emission of an organic emitting layer, have recently received much attention as a flat panel display device.
An organic light emitting diode display device includes a substrate with thin film transistors (TFTs) formed thereon, organic light emitting diodes (OLEDs) formed on the substrate, and an encapsulation layer formed so as to cover the OLEDs.
The TFT is formed in each of sub-pixel regions defined by intersections of gate lines and data lines. The OLED that includes a first electrode, an organic emitting layer and a second electrode is connected to the TFT formed in each sub-pixel region.
In such OLED display devices, holes supplied from the first electrode and electrons supplied from the second electrode are injected into the organic emitting layer by electrical signals of the TFTs to form electron-hole pairs. The electron-hole pairs drop from an excitation state to a ground state, thereby emitting light.
In this regard, the TFT may be an amorphous silicon TFT, an oxide TFT, an organic TFT, and a poly-silicon TFT. The amorphous silicon TFT uses amorphous silicon for a semiconductor layer, while the oxide TFT uses an oxide such as indium gallium zinc oxide (IGZO), zinc oxide (ZnO), titanium oxide (TiO), or the like for a semiconductor layer. The organic TFT uses an organic material for a semiconductor layer, and the poly-silicon TFT uses poly-silicon for a semiconductor layer.
FIG. 1 is a sectional view of a general oxide thin film transistor.
As shown in FIG. 1, the general oxide TFT includes a substrate 10, and a gate electrode 11, a gate insulating film 12, an oxide semiconductor layer 13, source electrodes 15a and drain electrodes 15b, and a passivation film 16. In this regard, the oxide semiconductor layer 13 has a weak chemical resistance and thus is susceptible to an etchant for forming the source electrodes 15a and drain electrodes 15b. Thus, an etch stop layer 14 is further formed on the oxide semiconductor layer 13. The etch stop layer 14 is formed of a material such as SiO2 or the like to prevent damage to the oxide semiconductor layer 13 when patterning the source electrodes 15a and drain electrodes 15b. 
In this case, however, a process of patterning the etch stop layer 14 is further performed, thus increasing the manufacturing costs and time, which results in a reduced manufacturing yield. In particular, when the etch stop layer 14 is formed on the oxide semiconductor layer 13, there is limitation in reducing the width of the etch stop layer 14 because an overlay margin has to be considered. Accordingly, the length of channels increases and thus it is difficult to drive the oxide TFT at a high speed. In addition, the size of oxide TFT increases due to the etch stop layer 14, and an aperture ratio of an OLED display device including such oxide TFTs decreases.